VO2max Intervals for Cycling, Which Sessions Work Best

James. Welcome to the WattPlan Podcast. I'm James. Family, work, chasing the odd podium, building WattPlan in whatever hours are left, and a sports science reading habit that's frankly out of control. Today it's the session everyone loves to hate. VO2max intervals. Thirty fifteens, fours, eights, fives. Which ones actually work, and how often should you ride them? Joining me is Lyra, an AI who's read the trials so you don't have to, and every one of them is linked in the show notes.

Lyra. Ha, the suffering episode. Straight answer, the formats with the best evidence are thirty fifteens and repeats of three to eight minutes, ridden twice a week for seven to ten weeks in the trials. But the bigger lesson is that the dose matters more than the format. How much hard work you actually complete beats which clever pattern you picked.

James. Okay, quick one for anyone newer than me. What are we actually training here?

Lyra. VO2max is the most oxygen your body can use in a minute. It's the ceiling on your aerobic engine. To push it up, you need to spend time close to that ceiling, and that's the whole game with these sessions. Time near the top, repeated, over weeks. Every format is just a different way of collecting those minutes.

James. Right, so start with the trendy one. Thirty fifteens. Thirty seconds hard, fifteen easy. Do they live up to the hype?

Lyra. In the trials so far, they look strong. The first is Rønnestad and colleagues, 2015, in the Scandinavian Journal of Medicine and Science in Sports. Cyclists rode either short intervals or long intervals, matched for effort, twice a week alongside easy riding, for ten weeks. Nine riders in the short group, seven in the long. VO2max rose 8.7 percent with the short intervals and 2.6 percent with the long ones. [1]

James. Hang on, that's more than three times as much. That's huge.

Lyra. It's a big gap, yes. And the same research group came back in 2020 with elite cyclists, VO2max around 73 millilitres per kilo per minute, so properly fit. Nine sessions in three weeks. The short session was three sets of thirteen thirty second efforts with fifteen seconds' recovery, against four five minute efforts. VO2max didn't change any more in one group than the other. But twenty minute power rose 4.7 percent after the thirty fifteens and fell 1.4 percent after the fives. [2]

James. So the thirty fifteens win. Surely that's the end of it? Why would anyone ride anything else?

Lyra. Because the trials are small. Nine riders here, seven there, and the spread in the results is about as big as the effects themselves. Nobody can be blinded to the session they're riding. The 2015 riders were all men, and the thirty fifteen trials all come from one research group. So it's a promising lead for trained riders. It isn't proof that thirty fifteens beat every long interval set.

James. Okay, fair. So what about the long stuff? Is longer better?

Lyra. Here's where it gets interesting. Stephen Seiler's group published a trial in the same journal in 2013. Thirty five trained recreational cyclists, twenty nine men and six women, split into four groups for seven weeks. One group rode easy only. The others did four by four, four by eight or four by sixteen minutes, twice a week, as hard as they could hold. [4]

James. And the winner was?

Lyra. Four by eight, clearly. Across peak oxygen uptake and two power measures, that group gained 11.4 percent on average, against 5.5 for four by four, 5.6 for four by sixteen and 4.2 for easy riding. And the bit I love is how. Thirty two minutes of work at about ninety percent of peak heart rate beat sixteen minutes at about ninety five percent, even though the eights felt easier.

James. Really? Easier and better? That breaks my brain a bit.

Lyra. It's the dose idea again. The fours were harder per minute, but there just weren't enough minutes. The eights let riders pile up twice the hard work at an effort they could sustain. Which is why our view at WattPlan is that dose beats format. Finish the session at full effort, and build towards fifteen to thirty minutes of hard work.

James. So if I'm hearing you right, the thirty fifteens are the exciting new kid, but the real rule is finish the session and stack up the minutes.

Lyra. That's it exactly. And treat the thirty fifteens as a lead from small trials, not settled science. One more honest gap. Nobody has compared thirty fifteens with four by eights head to head, and the two trials that favoured each one used different riders and different matching. So we genuinely don't know which of those two is better.

James. Okay, numbers. What power should these actually be?

Lyra. In WattPlan's zones, VO2max is Zone 5, 106 to 120 percent of your FTP. At an FTP of 250 watts, that's 265 to 300 watts. Longer reps mostly sit lower in the band, so the library rides five minute efforts at 110 percent, most four minute efforts at 110 or 112, and two minute efforts at 115. Thirty second efforts run higher. The library's Billats sit at 120 percent, so start any thirties there and adjust until you can repeat them to the last one.

James. And the fifteen seconds in between? Do I just stop?

Lyra. No, keep pedalling easily. The library's thirty thirties and forty twenties recover at half your FTP. And this is where the turbo earns its keep. In ERG mode the trainer holds each target for you, which suits Billats and forty twenties. On the road, junctions and traffic wreck a short recovery, so save the road for three to five minute efforts on a steady climb.

James. Let's split it by who's listening. If you're new to this, should you be doing any of it?

Lyra. If you're new to structured training, not yet. Build a base of endurance and sweet spot first. That's how WattPlan plans work too. Base phases and beginner plans stay on sweet spot, and harder work, threshold and for most riders VO2max, comes in from the build phase. These sessions pay off far more once you've got the aerobic base underneath them.

James. And if you train with power?

Lyra. If you train with power, confirm your FTP first, so the 106 to 120 percent targets mean something. Then ride the VO2max sessions your plan gives you. A WattPlan plan sets at most one a week, never next to another hard day, and changes the format from week to week. That's how WattPlan plans it, because the dose matters more than the format, and the plan builds the hard minutes as the block goes on.

James. And if you race, or you're chasing a target?

Lyra. If you race, the thirty fifteen evidence is mostly in riders like you, trained and competitive. The elite riders managed three sessions a week, but only for three weeks, and that's more than a WattPlan plan asks of you. The plan keeps it to two hard days a week at most, every fourth week easier, and never two hard days back to back.

James. One thing I noticed. There's no thirty fifteen in the WattPlan library. Isn't that a bit awkward?

Lyra. It's an honest gap, yes. The library has ten VO2 Max workouts, including Billats, which are thirty seconds on and thirty off, and forty twenties. But we found no published trial reporting fitness gains from forty twenties in cyclists. The library's longer reps, three to five minutes, are the ones closest to the trials.

James. So what's the homework?

Lyra. Three things. One, test or confirm your FTP. Two, ride the VO2max sessions your plan gives you at full effort, and finish them rather than chase a cleverer format. Three, retest your best five minute power at the end of the block. Responses vary a lot between riders, so your own five and twenty minute power is the best test of whether the block worked.

James. Okay, in my words. Get my FTP right, ride the VO2max sessions the plan gives me, finish every one, then retest and see if it actually did anything for me.

Lyra. Perfect. And the one line to keep, finish the session and stack the minutes. The format is the small print.

Lyra. The full article and every study we mentioned are on the WattPlan blog, linked in the show notes.

James. And if you want a plan that's built around the time you've actually got, that's what WattPlan does. Thanks for listening.

Voices produced with ElevenLabs. James's voice is a clone of his own, Lyra is an AI voice, and James reviews every script before it is published.